This invention relates to stalling a programmable processor.
“Pipelining” is a technique used in conventional programmable processors, such as digital signal processors, in which instructions are overlapped in execution in order to increase overall processing speed. A pipelined processor typically processes instructions in a number of stages. An instruction moves from one stage to the next according to a system clock, which typically has a clock rate determined by the slowest stage in the pipeline.
While processing instructions, conditions, called “hazards,” sometimes prevent the next instruction in the instruction stream from executing. For example, a data hazard arises when an instruction depends on the results of a previous instruction that has not finished from the pipeline. Hazards, therefore, cause the pipeline to “stall” and reduce the pipeline's performance.
One common solution is a hardware addition called a pipeline interlock, which detects a hazard and stalls a pipeline until the hazard has cleared. Typically, the pipeline interlock stalls the pipeline by inserting a special instruction, commonly called a “NOP,” that requires no operation from the pipeline but consumes a slot in the instruction stream.